In certain machining applications, it is sometimes desirable to locate two cutting tools aligned on a common axis at a single tooling station. This is sometimes done in producing certain parts having concentric features on the part, with separate cutting tools required to machine each feature. An example of such an application is the machining of valve stem guide bores and the corresponding valve seats in an engine cylinder heads with a reamer and valve seat finishing tool located to relate on a common axis.
In this instance, it is advantageous to machine both the valve stem guide and the valve seat at a single station because the concentricity of the seat and bore may be more easily maintained, and it also reduces the number of machining stations required.
Arrangements are known in which a valve seat finishing tool and reamer are concentrically mounted at a single station, with the reamer axially advanced independently of the spindle assembly by which the tooling is rotated, and also rotated at a different speed than the valve seat finishing tool in order to maintain the valve seat finishing tool, in order to machine the valve stem guide bores.
This independent axial motion of the reamer has been accomplished by a draw bar mounted in the spindle assembly carrying a reamer holder.
There also presently is an increased need for so called "flexible" machining equipment in which the tooling of high production machines may be changed quickly, such as for conducting operations on differently configured parts. In conventional transfer machines, the tooling is dedicated to a specific part and the transfer line must be retooled by a rebuilding of the machine to be adapted to the manufacture of another part.
In "flexible" machining applications, automatic tool changers have heretofore been employed which allow an exchange of tooling assemblies automatically in a spindle assembly at a given machining station. However, heretofore no tooling assembly has been provided having a plurality of separately driven cutting tools or having a separately moveable element which must be connected to a separately moveable actuator member in the spindle assembly.
It is also highly desirable in such applications in which separate tools are rotated at different speeds in the same assembly, that the concentricity of the separate cutting tools be maintained by minimizing the runout between the respective supporting tool holders and tool holder bodies.